Cards which can store information are widely used for various applications. Cards comprising a magnetic strip are well known but also other types, such as laser-recordable cards or cards comprising an electronic chip, sometimes called `smart cards`, are becoming increasingly popular.
Dil, in U.S. Pat. No. 4,209,804 teaches a reflective information recording structure which contains prepressed V-shaped grooves in Which data may be recorded by a laser causing local melting of the reflective metal coating. The data on the media is read by means of optical phase shift effects. Since the preformed grooves are at an optical phase depth of 950 to 1400, the reading laser must be of the precise wavelength corresponding to the groove depth. The information area has a width, depending on the wavelength of the recording beam, of 0.4 to 0.8 .mu.m and a thick protective substrate, usually 1200 .mu.m deep, is used to ensure that small dust particles are out-of-focus for the read beam.
Such thick protective materials cannot be used for wallet cards which have a total thickness of only 800 .mu.m under ISO standards. In addition, it would be uncomfortable to carry a thick, rigid card in trousers pockets or wallets. It is also difficult to laminate a phase sensitive recording/reading medium to a protective foil with an adhesive without introducing a varying phase shift across the surface. It is also impracticable to melt large holes since a large lip will be formed around the hole causing a great distortion of the phase shift. Edge transition of the hole is the phase shift which is measured, and since the height of the lip is directly proportional to the square root of the hole diameter, phase shift reading is only practical for small holes. For example, a 25 .mu.m diameter hole creates a lip of one .mu.m height, which is much larger than the wavelength of the reading beam. Thus for large holes and bonded protective materials it is desirable to have a recording/reading structure that does not rely on phase shifts.
Lahr in U.S. Pat. No. 3,873,813 teaches a debit card wherein a reflective heat sensitive material becomes transparent on heating, thereby exposing an underlying strip of black paper which then absorbs the light energy. Recording requires exposure to a high intensity light beam for 0.7 second to raise the temperature of the material to 80.degree. C. and an additional 5 milliseconds above 80.degree. C. This type of credit card system permits recording of less than two data bits per second. Because of the retained diffused liquid, the sizes of the data spots are large and difficult to control. This card requires a blue read beam, therefore scratches and surface dust may cause a large number of data errors unless very large data spots are used which reduce the capacity to less than 10,000 bits. While this data capacity is sufficient for some debit and credit cards, it is unsuitable for detailed recording of financial, insurance, medical and personal records. Also, the recording rate of less than two bits per second would make it unsuitable for most applications. Another disadvantage of said card is that all the data are destroyed at a temperature above 80.degree. C., for example when lying on the dashboard of a car or if passed through a household washer and dryer.
Nagata in U.S. Pat. No. 4,197,986, Girard in U.S. Pat. No. 4,224,666 and Atalla in U.S. Pat. No. 4,304,990 teach updating of data cards. Nagata teaches the updating of maximum limits and balance on a card in which the complete data file is kept in an auxiliary memory circuit such as a magnetic disc or drum. A sales slip containing the transaction is recorded separately from the card. Girard teaches a data-processing machine-access card containing an integrated circuit chip with a memory bank. The memory stores predetermined items of confidential data intended to authorize or prevent access to the machine. Only the balance is updated. Atalla teaches a card on which only the balance is recorded and updated. This card can only be used where the transaction system is connected to a central computer. None of these cards has the memory storage capacity needed to accumulate records of past transactions.
Drexler in U.S. Pat. No. 4,542,288 teaches a method for making a data card involving photolithographically pre-recorded information, such as reference position information or servo tracks, on a strip of a high resolution, direct-read-after-write laser recording material, then adhering the strip to a card such that the strip is recordable in place. A protective transparent laminating material is bonded to the recording surface and then user information is recorded on the strip using a laser which is focused on the strip through the laminating material. This laminating material is preferably polycarbonate which has the disadvantage that it does not adhere well to the recording layer.
A major disadvantage of the prior art laser recording materials is their susceptibility to mechanical impact which may cause defects such as scratches and may result in a considerable loss of the recorded data. In addition, most of these data cards comprise a plastic foil as protective layer on top of the recording medium. The life-time of such recording materials, which is required to be 10 years for some applications, is insufficient because the plastic foil is not an efficient barrier against solvents, oxygen, moisture and other potential causes of data loss.